For many type of light source assemblies heat spreading and heat exchange of the heat generated by a light source, such as a LED, of the light source assembly rely on the size of the substrate onto which the light source is assembled and the heat exchange between the substrate and the gas surrounding the light source assembly. This is especially true for light source assemblies arranged within an envelope in the form of a bulb, e.g. a light bulb. For such a bulb design the heat exchange between the light source assembly and the surroundings rely on the mere heat exchange between the substrate acting as a heat spreader and the gas enclosed in the bulb as well as thermal radiation, as heat management through conduction along wire (stem) connections is largely negligible.
For proper heat exchange of heat generated by the light source sufficient surface of the substrate acting as the heat spreader is needed. Also a good thermal interface between light source and the heat spreader is required. Prior art rely on a large substrate surface around the light source for enhancing the heat exchange between the substrate acting as a heat spreader and the gas. However, such a set-up will block light from the light source that is directed towards the surface of the substrate.